Moving electric current collectors



Oct. 13, 1964 s. FOLDES ETAL 3, 3, 3

MOVING ELECTRIC CURRENT COLLECTORS v Filed March so; 1961 INVENTORS S HEN FOLDES ADO J. WESOLOWSKI BY 7 fl4-M ru M ATTORN EV United States Patent Office 3,153,163 Patented Oct. 13., 1964 MCVING ELECTRIC CURRENT COLLECTORS Stephen Foldes, Cincinnati, Ohio, and Adolph J. Wesolowski, Phoenix, Aria, assignors to General Electric Company, a corporation of New York Filed Mar. 30, 1961, Ser. No. 99,528 12 Claims. (Cl. 310-231) This invention relates to moving or sliding current collectors, such as slip rings, commutators, and the like. More particularly, it relates to such current collectors or transmitters which are characterized by increased life under both normal atmospheric and high altitude conditions.

It is well known that the brushes of electrodynamic machines operating at elevated altitudes wear very rapidly from contact with their current collectors. Among the means which have been used to decrease such Wear have been the use of brushes having additives, such as metal sulfides, silver salts, etc., which are added to the carbon brush in various ways, such as in a core or flakes or chunks or particles or as impregnants distributed throughout the body of the brush. While such treated brushes constitute an improvement over plain brushes, it has been found that brush wear is still excessive. Similar excessive wear occurs when the electrical equipment is subjected to vibration. 7

It is, therefore, a principal object of this invention to provide means for increasing the life of brushes operating at normal and elevated altitudes.

Briefly, the invention comprises the use with carbon brushes of commutator or slip ring structures which in contrast to the usual copper, bronge, steel, silver or cast iron consist of sintered mixtures of, by weight, from 25 percent to 75 percent silver with the remainder tungsten carbide or tungsten.

Those features of the invention which are believed to be novel are set forth with particularity in the claims appended hereto. The invention will, however, be better understood and further objects and advantages thereof appreciated from a consideration of the following description of the drawing in which:

FIGURE 1 is a schematic representation of slip rings made according to this invention and FIGURE 2 is a similar drawing of a commutator structure made of the present materials.

It has been found that while silver fulfills many of the requirements of an ideal moving or sliding current collector in that it has good electrical and thermal conductivity, is an excellent lubricant material and serves as a good bearing surface for carbon brushes, its softness and low vaporization. point cause it to erode very rapidly especially at high altitudes or under vibration and develop the threads or grooves which are characteristic of such metals when used for such purpose. Copper is possessed of much the same characteristics as silver and is limited by the same deficiencies. Such roughness excessively wears the carbon brushes used therewith.

It has been found that mixtures of from about 25 percent to 75 percent, by weight, of silver withthe remainder tungsten carbide or tungsten serve very admirably as materials for moving currentcollectors. Such materials exhibit suificient electrical conductivity for the purpose by reason of their silver content. Likewise, they have good bearing and lubricant properties. The percent materials, furthermore, do not vaporize under arcing and produce the ionized path between brush and current collector which gives rise to the surface roughness, threads or grooves characteristic of copper and other metal-containing current collectors which excessively wear brushes. The presence of the hard metal further enhances the Wearability of the structure.

The current collectors of the present invention are conveniently prepared by sintering methods. For example, the powdered silver and tungsten carbide or tungsten is thoroughly mixed and pressed'into a suitably shaped blank under a pressure of from about 40 to tons per square inch. The compacted material is then sintered at temperatures ranging from about 1 000 C. to about 1500" C. While a temperature of 1050 C. will suitably sinter the material and cause the silver to flow throughout the skeleton of tungsten carbide or tungsten, temperatures of from about 1450 C. to 1500 C. have been found to improve the electrical conductivity and mechanical characteristics of the structures. It has also been found that the tungsten carbide or tungsten alone may be compacted under pressures as above, sintered at temperatures above 1800 C., and then dipped in molten silver so that the latter infiltrates through the skeleton of harder material and completely fills the pores. After the blank has been prepared, it is machined as desired to provide moving current collectors as of the slip ring or collector type. Of course, in some instances thematerial can be sintered in or close to its final size and shape.

Typical cur-rent collector structures are shown schematically in the drawing. Referring to FIGURE 1, there are shown slip rings 1 and 2 with carbon brushes 3 and 4 mounted thereon by means not shown, the slip rings being connected in circuit as desired by means ofleads 5 and 6. FIGURE 2 shows a simplified commutator structure 7, having segments 8 insulated one from the other in the usual fashion and mounted in sliding contact with the commutator surface, carbon brushes 9 and 10.

Slip rings of various compositions were prepared by the sintering method described above and tested using carbon brushes with various additives to determine the effect of the various materials on carbon brush wear. The slip rings of silver, tungsten and tungsten carbide .were 2 /8 inches in diameter, while the silver and molybdenum rings were 2% inches in diameter, all rings being rotated at a speed of 7200 rpm. Brushes having a cross section of /2" x A surface contact were 'used with a pressure of 8 p.s.i. against the ring. A

current of 30 amperes was passed through the rings in all cases.

Shown in the table below for carbon brusheshaving a molybdenum disulfide additive in various forms are the hours of ope'ration under the above conditions to produce A1" of brush wear. I

Hours Life Per $4" Wear of Brush (T464) Carbon (R776) Carbon (R710) Carbon Comp. (by wt.) wJMoSz Core xvi/M082 w./MOSz Chunks Flakes Air, N 2, Air, N2, Air, NZ, Hrs. Hrs. Hrs. Hrs. Hrs. Hrs.

l, 250 3, 910 3, 200 1, 050 r 2, 350 1, 250 2, 500 910 1, 000 1, 500 8,000 1,700 2, 200 740 1, 300 '1, 020 2, 650 1, 300 2, 700 1, 400 270 890 2, 600 850 380 507 Ag 2 M0 730 3, 200 750 600 555 1, 225

From the above table, it will be quite obvious that the compositions containing silver and tungsten carbide or tungsten are far and away superior to those of copper and tungsten or silver and molybdenum, particularly when it is considered that such brushes in practical usage must operate at both normal altitudes and at elevated altitudes.

There are provided then by the present invention moving or rotatable electric current collectors which are characterized by adequate electrical conductivity resulting in a minimum potential drop between brush and collector. They are hard enough to resist threading and other surface wear while at the same time providing a good bearing surface to minimize brush wear. The boiling point of the harder constituents, that is, tungsten carbide or tungsten, is high enough to minimize vaporization under arcing conditions with its resulting threading of the collector surface. The silver content of the collector serves as a good lubricant and bearing surface to enhance their favorable characteristics. These characteristics of the present moving or sliding current collectors make them particularly useful as slip rings or commutators, generally for electrodynamic machinery and particularly so for such machinery which is subjected to vibration or other conditions, such as high altitudes, which cause excessive corrosion of brushes. Likewise, they are particularly adaptable to machinery which is characterized by high operating speeds.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric current conducting device of the rotating type utilizing carbon brushes, a rotatable current collector consisting throughout of a sintered mixture containing by weight firom about 25 to 75 percent silver with the remainder chosen from the group consisting of tungsten carbide and tungsten.

2. A device as in claim 1 wherein said collector consists of by weight from about 25 to 75 percent silver with the remainder tungsten carbide.

3. A device as in claim 1 wherein said collector consists of by weight from about 25 to 75 percent silver with the remainder tungsten.

4. A device as in claim 1 wherein said collector conisists of by weight from about to 65 percent silver with the remainder chosen from the group consisting of tungsten carbide and tungsten.

5. A device as in claim 1 wherein said collector consists of by weight about 35 to 65 percent silver with the remainder tungsten carbide.

6. A device as in claim 1 wherein said collector contains by weight about 35 to 65 percent silver with the remainder tungsten.

7. A device as in claim 1 wherein said collector consists of by weight about 35 percent silver and 65 percent of a material selected from the group consisting of tungsten carbide and tungsten.

8. A device as in claim 1 wherein said collector consists of by weight about 35 percent silver and 65 percent tungsten carbide.

9. A device as in claim 1 wherein said collector consists of by weight about 35 percent silver and 65 percent tungsten.

10. A device as in claim 1 wherein said collector consists of by weight about 5 0 percent silver and percent of a material selected from the group consisting of tungsten carbide and tungsten.

11. A device as in claim 1 wherein said collector consists of by weight about 50 percent silver and 50 percent tungsten carbide.

12. A device as in claim 1 wherein said collector consists of by weight about 50 percent silver and 50 percent tungsten.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,070 Hensel Mar. 9, 1943 2,504,906 Trumbly Apr. 18, 1950 2,864,921 Graves Dec. 16, 1958 2,895,033 Favre July 14, 1959 2,998,641 Atkinson Sept. 5, 1961 

1. IN AN ELECTIC CURRENT CONDUCTING DEVICE OF THE ROTATING TYPE UTILIZING CARBON BRUSHES, A ROTATABLE CURRENT COLLECTOR CONSISTING THROUGHOUT OF A SINTERED MIXTURE CONTAINING BY WEIGHT FROM ABOUT 25 TO 75 PERCENT SILVER WITH THE REMAINDER CHOSEN FROM THE GROUP CONSISTING OF TUNGSTEN CARBIDE AND TUNGSTEN. 